1. Field of the Invention
The present invention relates to an image forming apparatus and an output control method of the same, and more particularly, it relates to an image forming apparatus having an output processing device connected thereto and an output control method of the same for optimizing productivity of the overall apparatus.
2. Description of the Related Art
A known image forming apparatus having an output processing device detachably fixed thereto has a structure in which a paper-transport controller including a paper-transport controlling CPU is provided so as to supervise movements of both sheets of paper in the image forming apparatus and the output processing device in a centralized manner. The paper-transport controller employs a method for achieving the maximum throughput by determining a paper process time of the output processing device, paper transport speeds in the image forming apparatus and the output processing device, the lengths of a paper transport route and the sheet of paper, and an optimal print timing in accordance with the corresponding print mode (e.g., see Japanese Patent Laid-Open No. 9-39341, corresponding to U.S. Pat. No. 6,373,581).
That is, the known image forming apparatus disclosed in the above patent document includes timing-determining means for determining a timing of the following print command on the basis of a job schedule transmitted from an image-information controller, and the paper-transport controller unit includes timing-measuring means for measuring a timing for starting a print job thereat. With this arrangement, a CPU of the paper-transport controller shares a load to be processed by a CPU of the image-information controller. As a result, the process load is dispersed, thereby achieving improved speed of a print operation as a primary function of the image forming apparatus.
Also, an image forming apparatus proposed, e.g., in Japanese Patent Laid-Open No. 2004-271627 (corresponding to U.S. Application No. 2004-247336) has a structure in which a print operation thereof is controlled by transmitting an output-reservation command (reservation information) to the output processing device connected to the image forming apparatus and receiving a paper output interval from the output processing device, ranging from acceptance of the reserved sheet of paper to a possible acceptance of the following sheet of paper, both of the output processing device.
Unfortunately, with the above-described known structures, when a part of reserved information is canceled, the following problems may occur. That is, in the above-described known examples, information about print jobs serving as reservation information about a plurality of print jobs is transmitted to the output processing device. In other words, a plurality of pieces of print job information including a print job in process and another print job to be subsequently processed is transmitted to the output processing device.
For example, the output processing device recognizes an output process time on the basis of the transmitted print job information and, taking into account the output process time, controls the transport interval of a sheet of paper for the following print job. Thus, when print job information of a plurality of pieces of print jobs is canceled (deleted) midway through its execution, the output process times thereof are also canceled. Hence, the transport interval between the sheets of paper for the present and the following print jobs must be adjusted. Accordingly, after confirming that the print job in process is completely processed, the following print job must be processed, thereby causing a longer interval between the print jobs and resulting in decreased productivity.
When print job information is cancelled, continuing the process of the print job causes a paper jam between the sheet of paper in process and the following sheet of paper.